(a) Field of the Invention
The present invention relates to an ink composition for spacer formation used for color televisions, computer monitors, and other display devices, and a spacer element using the same.
(b) Description of the Related Art
Demand for color liquid crystal displays has been on the increase in recent years, and large liquid crystal displays are being manufactured. However, manufacturing costs should be reduced in order for the color display devices to be used more widely.
Conventionally, a liquid crystal display is manufactured by forming a liquid crystal driving device, such as a TFT (thin film transistor), and a coloring device, such as a color filter, on a pair of opposing transparent insulating substrates. Between the substrates there are spacers that maintains a 3 to 10 μm space therebetween. Liquid crystal is injected in this space, and then the spacing is sealed to form a liquid crystal device.
Conventionally, spherical or cylindrical silica, alumina, or synthetic resin particles randomly distributed between the TFT substrate and the color filter substrate have been used as the spacer. But, in this case, the spacer around the light passage of the liquid crystal display may hinder driving of the liquid crystal or deteriorate the display quality due to the optical properties of the spacer itself.
In order to solve this problem, a method of selectively forming a spacer in the black matrix formation part through which no light passes, using a photoresist substance, has been proposed. In this case, the black matrix blocks the display quality-deteriorated part, and thus deterioration of display quality can be avoided.
However, when using a photoresist, the spacer formation process requires many steps including spin coating, pre-baking, exposure, developing, and post-baking of the spacer substance, and therefore the manufacturing cost increases.
To solve this problem, Korea Patent Publication No. 2001-0049941, Japan Patent Publication No. 2001-109002, and Japan Patent Publication No. 2001-83525 proposed a method for selectively forming a spacer on the black matrix through which no light passes, by the inkjet process.
Korea Patent Publication No. 2001-0049941 and Japan Patent Publication No. 2001-83525 proposed a cross-linking spacer-forming substance, which could be sprayed by the inkjet head, and which used a homopolymer or copolymer as a cross-linkable substance. Usage of the substance was limited from 0.01 to 30 parts by weight. During spacer formation, the sprayed solvent is evaporated in the cross-linking step, and only the homopolymer or copolymer forms the spacer. While the diameter of the ink droplet on the substrate surface remains almost the same due to its adhesivity, its height decreases, so that the height of the final spacer becomes significantly lower than that of the ink droplet. Accordingly, the height becomes insufficient for a high-resolution black matrix, which requires a small diameter.
In addition, Japan Patent Publication No. 2001-109002 proposed that it is preferable to use a monomer or oligomer with a low molecular weight, considering the spraying characteristics of the ink, while limiting the content of the solvent under 50 parts by weight and increasing the content of the spacer-forming substance. However, a substance with a low molecular weight does not have sufficient mechanical properties unless it is fully cross-linked, and light exposure or heat treatment for sufficient cross-linking increases manufacturing time and decreases productivity.